| Step | Hyp | Ref | Expression | 
						
							| 1 |  | segcon2 |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. \/ x Btwn <. A , B >. ) /\ <. A , x >. Cgr <. C , D >. ) ) | 
						
							| 2 |  | andir |  |-  ( ( ( B Btwn <. A , x >. \/ x Btwn <. A , B >. ) /\ <. A , x >. Cgr <. C , D >. ) <-> ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. A , x >. Cgr <. C , D >. ) ) ) | 
						
							| 3 |  | simpl1 |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> N e. NN ) | 
						
							| 4 |  | simpl2l |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> A e. ( EE ` N ) ) | 
						
							| 5 |  | simpr |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> x e. ( EE ` N ) ) | 
						
							| 6 |  | simpl3 |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) | 
						
							| 7 |  | cgrcom |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ x e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( <. A , x >. Cgr <. C , D >. <-> <. C , D >. Cgr <. A , x >. ) ) | 
						
							| 8 | 3 4 5 6 7 | syl121anc |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> ( <. A , x >. Cgr <. C , D >. <-> <. C , D >. Cgr <. A , x >. ) ) | 
						
							| 9 | 8 | anbi2d |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> ( ( x Btwn <. A , B >. /\ <. A , x >. Cgr <. C , D >. ) <-> ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) | 
						
							| 10 | 9 | orbi2d |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> ( ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. A , x >. Cgr <. C , D >. ) ) <-> ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) ) | 
						
							| 11 | 2 10 | bitrid |  |-  ( ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) /\ x e. ( EE ` N ) ) -> ( ( ( B Btwn <. A , x >. \/ x Btwn <. A , B >. ) /\ <. A , x >. Cgr <. C , D >. ) <-> ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) ) | 
						
							| 12 | 11 | rexbidva |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. \/ x Btwn <. A , B >. ) /\ <. A , x >. Cgr <. C , D >. ) <-> E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) ) | 
						
							| 13 |  | brsegle2 |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( <. A , B >. Seg<_ <. C , D >. <-> E. x e. ( EE ` N ) ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) ) ) | 
						
							| 14 |  | brsegle |  |-  ( ( N e. NN /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) ) -> ( <. C , D >. Seg<_ <. A , B >. <-> E. x e. ( EE ` N ) ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) | 
						
							| 15 | 14 | 3com23 |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( <. C , D >. Seg<_ <. A , B >. <-> E. x e. ( EE ` N ) ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) | 
						
							| 16 | 13 15 | orbi12d |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( ( <. A , B >. Seg<_ <. C , D >. \/ <. C , D >. Seg<_ <. A , B >. ) <-> ( E. x e. ( EE ` N ) ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ E. x e. ( EE ` N ) ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) ) | 
						
							| 17 |  | r19.43 |  |-  ( E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) <-> ( E. x e. ( EE ` N ) ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ E. x e. ( EE ` N ) ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) | 
						
							| 18 | 16 17 | bitr4di |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( ( <. A , B >. Seg<_ <. C , D >. \/ <. C , D >. Seg<_ <. A , B >. ) <-> E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. /\ <. A , x >. Cgr <. C , D >. ) \/ ( x Btwn <. A , B >. /\ <. C , D >. Cgr <. A , x >. ) ) ) ) | 
						
							| 19 | 12 18 | bitr4d |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( E. x e. ( EE ` N ) ( ( B Btwn <. A , x >. \/ x Btwn <. A , B >. ) /\ <. A , x >. Cgr <. C , D >. ) <-> ( <. A , B >. Seg<_ <. C , D >. \/ <. C , D >. Seg<_ <. A , B >. ) ) ) | 
						
							| 20 | 1 19 | mpbid |  |-  ( ( N e. NN /\ ( A e. ( EE ` N ) /\ B e. ( EE ` N ) ) /\ ( C e. ( EE ` N ) /\ D e. ( EE ` N ) ) ) -> ( <. A , B >. Seg<_ <. C , D >. \/ <. C , D >. Seg<_ <. A , B >. ) ) |